A Study on Recovery from Potentially Lethal Damage Induced by γ-Irradiation in Plateau-phase vero Cells in vitro

방사선 조사후 발생한 잠재치사손상의 회복(PLDR)에 있어 조사선량 및 시간에 따른 환경변화가 회복의 동적양상에 미치는 영향을 Vero 세포계를 이용하여 실험하였다. 배양액을 교환시키지 않고 배양하여 평형기에 도달한 세포에 동물실험용 세시움 조사기로 1Gy~9Gy의 감마선을 조사하고 각 조사조건에서 0~6 및 24 시간동안 정치지킨 후 Agarose가 포함된 새로운 배양액에서 배양하였다. 16Gy를 조사한 동종의 세포를 feeder 세포로 첨가하여 배양액내의 전체세포수를 일정하게 한 조건에서 형성된 세포집락수에 따라 세포의 생존을 정하였다. 잠재치사손상의 회복은 2~4시간 정치후에 포화수준에 도달한 빠른 회복이었다. 방사선량이 증가함에 따라 회복속도는 증가하였고, 포화수준의 회복량도 증가하였다. Linear-quadratic model에 의한 ‘방사선량-생존분획’ 분석결과 잠채치사손상이 회복됨에 따라 일차 비활성계수 α는 급속히 감소하여 0에 접근하였고 이차 비활성계수 ß는 미미하게 증가하여 PLDR은 α로 표시되는 손상에 주로 영향을 주었다. Multitarget model에 따라 분석한 결과 Do는 변화가 없고 Dq가 증가하였다. 세포 생존분획이 높은 3 Gy 이하의 저선량 영역에서 dose modifying factor가 높아 잠재치사손상의 회복에 의한 영향이 저선량 영역에서 상대적으로 크게 나타났다.

Recovery from potentially lethal damage (PLDR) after irradiation was studied in plateau-phase culture of Vero cells in vitro. Unfed plateau-phase cells were irradiated wth dose of 1 to 9 Gy using Cs-137 irradiator. Cells then were incubated again and left in situ for 0,1,2,3,4,5,6, and 24 hours and then were trypsinized, explanted, and subcultured in fresh RPMI-1640 media containing 0.33% agar. Cell survival was measured by colony forming ability. An adequate number of heavily irradiated Vero cells were added as feeder cells to make the total cell number constant in every culture dish. As the postirradiation in situ incubation time increased, surviving fraction increased by PLDR. The rate of PLDR was so rapid that increased surviving fraction reached saturation level at 2 to 4 hours after in situ incubation. As the radiation dose increased, the rate of PLDR fastened and the magnitude of increased surviving fraction at saturation level by PLDR also increased. In analysis of cell survival curve fitted to the linear-quadratic model, the linear inactivation coefficient (α) decreased largely and reached nearly to zero but the quadratic inactivation coefficient (ß) increased minimally by increment of postirradiation in situ incubation time. So PLDR mainly affected the damage expressed as α. In the multitarget model, significant change was not obtained in Do but in Dq Therefore, shoulder region in cell survival curve was mainly affected by PLDR and terminal slope was not influenced at all. And dose-modifying factor by PLDR was relatively higher in shoulder region, that is, in low dose area below 3 Gy.